Process of rolling steel in inert gas enclosures



M. C. VINTHER Dec. 14, 1943.

PRQCESS OFROLLING STEEL IN INERT GAS ENCLOSURES Filed April 2l, 1941 C PEs/MER,

e Lwwvi .Mm/AEL N' "Re IIL Dec. l14, 1943.

. M.Ac VINTHER PROCESS OF ROLLING STEEL IN INERT GAS ENCLOSURES Filed April 21, 1941 sheets-sheet 2 Patented Dec. 14, 1943 moet PROCESS OF ROLLING STEEL IN INERT GAS ENCLOSURES Michael C. Vinther, Torrance, Calif. Application April 21, 1941,.Serial No. 389,506

20 Claims.

This invention relates to a process of rolling steel or iron, and it has particular relation to a process for rolling hot steel or iron in' an inert gas enclosure, and may be used for hot rolling of other metals, such as copper and nickel and ltheir alloys.

The main object of my invention is to keep the atmosphere surrounding the rolling mill in such a condition that it will not cause oxidation or scaling of the metal which is being rolled. Another object of my invention is to keep the atmosphere surrounding the mill suiiiciently cool so that the operators of the mill can work in said atmosphere. A further object of my invention is to provide a process for circulating and treating the gas used in the mill enclosure so that the rolls of the mill can be cooled externally without causing oxidation of the metal being rolled, thus permitting the use of solid rolls in the mill. These and further objects of my invention will more fully appear from the following description. taken in connection with the accompanying drawings.

When steel or iron is formed into commercial form, it is usually done by rolling a large body of hot steel which has ilrst been heated to a high temperature, sometimes as high as about 1100 degrees centigrade. If the rolling is performed in the ordinary atmosphere, which contains oxygen and traces vof water vapor and carbon dioxide, there is a Continous oxidation of the hot surface of the steel, which causes ay loss of 'steel as rust or scale and necessitates subsequent pickling or acid treatment of the steel in order to remove the scale. This scale formation is an especially costly waste when the surface area per ton of rolled steel is large, as in the case of sheet,

strip, or wire rod. i

The oxidation is caused mainly by oxygen in the air and to a lesser degree by moisture in the atmosphere. Carbon dioxide will also cause some oxidation if it is present in the atmosphere.

The present invention, by circulating and treating the atmosphere surrounding the mill, improves the process of rolling hot-steel or other metal so that oxidation and scaling are partly 0r entirely eliminated during the rolling process.

'I'he idea of hot rolling of steel in an inert atmosphere is not entirely new, as this has been proposed for rolling wire rods and also for rolling hot slabs intoshee'ts. So-far as I am aware, however, none of the proposed plans have ever been carried into successful operation, chiefly due to the fact that they used hollow rolls, which have proved to be unsatisfactory because they lack strength and stiffness, and because the internal cooling of such rol1s` could not be regulated and controlled, and also because the mills had to be operated from outside the'inert gas enclosure.

When rolling hot steel or other metal in' an inert gas enclosure, there is the problem of cooling the enclosure, and also the problem of cooling the rolls, as there is a great deal of heat liberated from the hot metal and also from power converted into heat by the machinery.

It is extremely important to cool the rolls, for if they become too hot they will soften, lose strength and stiffness, and become distorted so that they will not roll the material into the exact shape desired. In the case of rolling sheet, then, it is often necessary to control the shape of the rolls by cooling the proper parts of the rolls. If, for instance, the middle of the roll becomes too hot, there will be irregular expansion of this part of the roll which will cause the rolled sheets to be too thin in the middle.

The prior art proposals for rolling hot steel in an inert atmosphere-used hollow rolls, through whichcooling water was passed in order to cool them. This had several disadvantages. The most serious disadvantage of hollow rolls is that they have far less strength and stillness than solid rolls, so that less pressure can be applied during the rolling, and less rolling effect or reduction of the steel can be accomplished in each rolling, with the result vthat a larger number of rolls and roll stands would be required, thus inpensate for the worn part of the roll. But this was not accomplished by the hollow rolls, which had a xed internal cooling channel, which made the cooling effect evenly distributed throughout the whole length of the roll.

, 'I 'he prior art proposals for rolling hot steel in an inert gas enclosure did not cool the gas or vatmosphere used in the enclosure, with the result that the temperature would become so high that the operators of the mill could not stay in the enclosure and operate the machinery. Consequently, the machinery had to be operated from the outside, which is a disadvantage and rather impractical, since, so far as I am aware, no mill as 'coke oven gas ing moisture may has been operated without requiring some kind of manual work and attention.

The present invention overcomes the diiliculties of cooling the rolls without making them hollow, and also provides a process for regulating the temperature of the inert gas or atmosphere in the enclosure.

In accordance with the present invention, the rolls are cooled externally by spraying water or other cooling liquid directly on the rolls. This spray water will be converted into steam by contact with the hot iolls, and if nothing further were done, it would contaminate the inert gas enclosure so that the atmosphere therein would no longer be inert, but in my process I remove the gas or atmosphere from the enclosure, dry it. and return it to the enclosure. This may be done continuously, and in any event, this circulation and drying of the gas or atmosphere is performed at such a rate that the moisture content of the gas is kept at such a. low percentage that the gas or atmosphere remains substantially non-corrosive to the hot metal.

The water or other cooling liquid may be sprayed on the outside of the rolls in any suitable way. I may use xed s'pray nozzles above the top roll, or spray nozzles on the side of the rolls, arranged so that the water falls on both the top and lower rolls. The spray nozzles may also be attached to a flexible hose, so the water can be directed against any desired part of the rolls. Steam may be used instead of water.

Instead .of water spray or steam, I may use a spray of any other liquid which is vaporized by contact with the hot rolls and which is substantially inert in contact with the hot steel or iron, such as for instance trichlorethylene and tetrachlorethane. Since these liquids are of high cost, the vapors will be recovered forre- `use by condensing in a cooler, or I may use any suitable absorber for recovery of the vapors. Liquid nitrogen may also be used to spray on the hot rolls, which will not only cool the rolls, but also supply inert gas for the mill enclosure.

In accordance with the present invention, the inert gas used in the enclosure is also cooled, thereby making it possible for the operators of the mill to vwoaakinside the enclosure. These` operators may use hose or oxygen breathing apparatus for respiration.

y-The inertgas to be used-in the mill enclosure fmay be produced or natural gas, or I may. use the nue gas from a boiler plant or furnace,A The combustion gas or flue gas isl iirst cooled to condense out most of the moistureandremove dust. 4I'he carbon dioxide is next removed, which may for example be done by absorption in a solution of alkali carbonate-or an organic amine solution such as monoethanolamne. The remainbe removed by passing the gas through a layer of activated aluminum oxide, or by any other suitable means of air drying.

For example, by combustion of natural gas, we may obtain a hot combustion gas of the composition: 22% .water vapor, 10% carbon dioxide and 0.5% carbon monoxide, the rest being nearly all nitrogen. By cooling to about degrees centigrade. most of the moisture will condense. The carbon dioxide is next removed by absorption in monoethanolamine or alkali carbonate.

During the rolling process, the gas in the mill enclosurey becomes hot and contaminated with moisture from spraying remove the gas, which, for example, contains by-cornbusti'on of a fuel such water on the rolls. so I,

3% water vapor and has attained a temperature of degrees centigrade, and pass it through a cooler, which may be a spray of cold water. so that the gas is, for example, cooled down to l5 degrees centigrade and contains only 11/2 volume percent of water vapor. This gas is returned to the inert gas enclosure.

If the gas in the mll'enclosure contains gases which are slightly oxidizing, such astraces of oxygen and carbon dioxide and water vapor from the cooling water applied to spray cooling of the rolls, then I make a correction by adding a reducing gas such as hydrogen, carbon monoxide or gas which is a mixture of those'gases, or a hydrocarbon gas such as methane.

For example, if the gas in the mill enclosure contains 3 volume per cent of water vapor and traces of carbon dioxide and oxygen, I add, for instance, 4 volume per cent of hydrogen, which will largely compensate for the oxidizing eifect of the moisture.

The gas used in the mill enclosure may be made to contain suicient hydrogen and carbon monoxide by using less than the theoretical amount of air for combustion in the combustion furnace, so that the hot flue gas .contains nitrogen, carbon dioxide, water vapor, hydrogen, and carbon monoxide.

I may also use liquid nitrogen to cool the rolls. I spray the liquid nitrogen on the hot rolls, and

. the vaporizations of it provides cooling and at the same time the gas produced from the vaporization furnishes the inert gas, an atmosphere of nitrogen. In case the liquid nitrogen does not sufficiently cool the gas or atmosphere inv the mill enclosure, the lgas may be circulated to a coolerand then returned to the mill enclosure, but no Vdrying of the gas will be necessary in this case because water is not used for cooling ofthe rolls.

In the accompanying drawings, I show one form of'apparatus for carrying my process into effect, and in which- Figure 1 is a diagrammatic plan view of a rolling mill enclosed in an inert gas enclosure, and apparatus for producing, treating, and circulating the inert gas, the top .of the inert gas enclosure being partly broken away to reveal the internal construction; and y Figure 2 is a sectional view of the rolling mill and the inert gas enclosure, taken along the line 2-2 of Figure l, and showing the water pipes and nozzles for spraying the rolls.

Referring to the drawings, I is an inert gas enclosure surrounding the entire rolling mill. It is a sulciently gas-tight enclosure built of any suitable material, such as for instance welded ysheet iron.l l2 is an opening for bringing in the hot steel or other metal to be rolled. A suitable conveyor may extend through this opening, which may be provided with asbestos skirts to prevent any great leakage of inert gas. 3 is a billet of hot steel or iron whichis being rolled into wire rod. l is the rolls for rolling the hot steel or iron. The rolls are placed in stands or housings and are provided with any suitable motors and drives. which are not shown. Neither do I show guides for leading the billet or rod being rolled.

5 is a coiler or reel for coiling or reeling the rolled steel, in this case a wire rod. There may be several reels or coilers, although the drawings show only one. 6 is the outlet where the rolled steel or metal is carried out' of the enclosure. It may be simply an asbestos skirt, or it may be a double door gate. 'I'here may be any suitable conveyor to carry the roller steel out of the inert gas enclosure I.

1 is a gas pipe, provided with a suitable valve Y 8, for supplying a gas such as natural gas to the combustion furnace. 9 is a pipe for supplying air to the combustion furnace. This pipe is provided with a suitable valve III. II is a combustion furnace for controlled combustion of gas. It may be provided with a. catalyst to use air low in oxygen. I2 is a cooler for the combustion gas where most of the moisture formed during combustion is condensed out by cooling. I3 is'a carbon dioxide absorber. It is a tower or agitator where the gas comes in thorough contact with a carbon dioxide absorbent such as alkali carbonate or a solution of organic amines. 'I4 is a drier, which may be a towercontaining a drying medium, such as activated alumina. I5 is an inert gas storage.

Leading from the gas storage I5 is a pipe I6 provided with a valve I1 and a fan I8. This pipe I6 connects with a pipe I9, which latter vpipe is situated over the top of the inert gas enclosure I and which is provided with several connecting pipes 2li leading into the top .of the enclosure I.

For removing the hot, wet, or contaminated gas from the mill enclosure I, I provide several branch pipes 2|, leading from the bottom of the inert gas enclosure I to a main pipe 22, which connects with pipe 23. This pipe 23 is provided with a fan 24 and a valve 25 and leads to the combined cooler and drier 26, whichmay bea tower with a. spray of lcold Awater which can cool the gas and at the same time condense the mois? ture. The spray water may be used again after it, for example, has been cooled by indirect cooling by water-from a cooling tower. To carry the cooled and dried gas back to the inert gas enclosure I, a, pipe 21 is provided which connects with the main gas inlet pipe I9 situated over the top of the mill enclosure I. Pipe 21 is provided with a suitable fan 28 and a valve 29.

To draw air from the mill enclosure I to the i combustion furnace II, I provide a pipe 30 which connects with pipe 23. This pipe 30 is provided with avalve 3I, a fan 32 and a valve 33.

Referring to Figure 2, pipe 34 is a. pipe for supplying steam, water or other liquid for cooling the rolls of the mill. Leading from the pipe 34 re branch pipes 35, provided with suitableI noz-v zles 3I5. If conditions require, these pipes may be used for steam or liquid nitrogen.

When starting up the system, when the inert gas enclosure I is lled With ordinary air, the supply of air for the combustion furnace II is drawn from the enclosure lI through branch pipes 2I, pipe 22, pipe 23, pipe 30, open valve 3|, fan 32 and open valve 33. .Valves I0 and 25 are closed. 'Gas is piped to the combustion furnace II through pipe 1 and open valve 8. The combustion gas-produced in furnace II is cooled and the moisture'condensed out vin cooler I2. The carbon dioxide is removed in carbon dioxide absorber I3, and the gas is further dried in drier I4. The dry inert gas is then passed to storage tank I5 and is passed further through pipe I5, -open' valve I1, fan I8 to pipe I9 and branch pipes 20- into the top of the mill enclosure I. I continue to draw air from themill enclosure-I through the bottom outlet pipe 22 to the combustion furnace I I and returnI it to the enclosure `I as an'inert gas of nearly pure nitrogen, until practically all of the oxygen has been removed from the .enclosure I.

The enclosure I is now in proper condition for rolling steel, and the rolling mill is set in motion. The metal to be rolled is heated to suitable rolling temperature, and is then carried into the mill enclosure I through opening 2 and passed between the rolls 4 to the reel 5 and out through opening 6. The rolled steel or metal should preferably remain in the inert gas enclosure I until it has cooled to a temperature at which it will not oxidize or scale when exposed to ordinary atmosphere.

During the rolling process, the rolls 4 are cooled When required by spray water from nozzles 36. Since the gas in the enclosure I tends to become hot and wet during the rolling process, it is drawn out through branch pipes 2I, pipe 22 and is carried through pipe 23 by fan 24 and through open valve 25 to the cooler and drier 26, where the gas is cooled and a part or all of the moisture is removed. During this operation the valve 3l is closed.

Fromvthe cooler and drier 26, the gas passes through pipe 21, fan 28 and open valve 29 toA pipe I9, from which it passes through branch pipes 20 and back into the top of the mill enclosure I. Thus, a complete circuit is established for the inert gas, in order that it may be kept in proper condition.

In order to compensate for unavoidable losses of inert gas, I then burn gas from gas line 1, and air from open valve I0, in the combustion furnacel II, and the gas thus produced is passed through cooler I2, carbon dioxide `absorber I3, drier I4, to storage I5, and the necessary amount is passed through pipe I6 and valve I1 to pipe I9, branch pipes 20, into the top of the mill enclosure I. v

If, for some reason, the inert gas in the enclosure I becomes contaminated with oxygen,

valve 25 is closed, valves 3I and 33 are opened,Y

and the gas is passed back to the combustion furnace II where it is mixed with the correct proportion of gas from the pipe 1 and burned, and

the gas thus produced is passed through cooler I2, carbon dioxide absorber I3, drier I4, to storage I5, pipe I6, valve I1, to pipe I9 and branch ,pipes 2|) into the mill enclosure I.

It will be readily understood by those skilled in the art that by using the proper number and the proper shape of rolls, we can roll any shape of steel, and that the aforesaid process for maintaining the inert atmosphere and cooling the rolls can be adapted to the rolling of any shape of steel or other metal without departing from the scope of my invention. Furthermore, it is obvious that the showing of the apparatus is very diagrammatic, and that modifications may be made in the apparatus without departing from the spiritof the invention. For example, the gas vinlet pipe I9 and branch pipes 20 may be located Having thusdescribed my invention, what I Iclaim is:

v1. In a process of-rolling hot metal in an inert gas enclosure, the steps -which include cooling the rolls externally by water, removing the gas from the enclosure, drying said gas, and returning said gas to said enclosure.

2.- In a process ofY rolling hot steel in an inert gas enclosure, the steps which include cooling the rolls externally by water, removing the gas from the enclosure, drying said gas, and returning said gas to said enclosure.

3. In a process or rolling hot metal in an inert gas enclosure, the steps which include cooling the rolls externally by water, continually removing the gas from the enclosure, drying said gas, and returning said gas to said enclosure.

'4. In a process of rolling hot metal in an inert gas enclosure, the steps which include cooling the rolls externally, removing the gas from the enclosure, cooling said gas, and returning said sas to said enclosure.

5. In a process oi rolling hot metal in an inert gas enclosure, the steps which includecooling the rolls externally, continually removing the gas from the enclosure, cooling said gas, and returning said gas to said enclosure.

6.*In a process of rolling hot metal in an'inert gas enclosure, the steps whichinclude cooling the rolls externally by water, removing the gas from the enclosure, cooling and drying said gas, and returning saidl gas to said enclosure.

'1. In a process of rolling hot metal in an inert vgasenclosure, the. steps which include external cooling of the rolls by water, removing the gas from the enclosure before it becomes appreciably corrosive to the hot metal, drying said gas, and returning said gas to said enclosure.

8. Ina process of rolling hot metal in an inert vgas enclosure, the steps which include external l. In a'process of rolling hot metal in an inert Y gas enclosure, the steps which include external cooling of the rolls by water, removing the gas from the enclosure, drying said gas, returning said gas to said enclosure, and correcting said gas for the harmful eiiect oi any remaining moisture by the addition of carbon monoxide as a reducing gas.

12. In a process of rolling hot metal in an inert gas enclosure, the step which consists in exl ternally cooling the rolls of the mill by a spray oi liquid nitrogen.

13. In a process of rolling hot metal in an inert gas enclosure, the steps which include externally cooling the rolls of the mill by a spray of liquid nitrogen, removing the gas from the enclosure, cooling said gas, and returning said gas to said enclosure.

14. In a process of rolling hot metal in an in ert gas enclosure. the steps which include cooling the rolls externally by a spray of an inert liquid which evaporates in contact with the hot rolls, removing the gas from the enclosure, cooling said gas, recovering said inert liquid, and returning said gas to said enclosure.

15. In a process of-rolling hot metal in an inert gas enclosure, the steps which include cooling the rolls externally, removing the gas from the enclosure when it becomes contaminated with oxygen, burning said contaminated gas with a correct proportion of a carbonaceous fuel, cooling the gas thus produced, removing the carbon dioxide from said gas, drying said gas, and returning said gas to said enclosure.

16. In a process of rolling hot metal in an inert gas enclosure. the step winch consists in externally cooling the rolls of the mill by a spray ot water, and drying said gas.

17. The herein-described method for the treatment of metal, which consists in introducing the metal in a hot rollable state to an enclosed atmosphere, maintaining the atmosphere inert, rolling y in the enclosure is maintained low to the point by the addition of a hydrocarbon gas as a reducing gas.

l1. In a process of rolling hot metal in an inert -gas enclosure, the steps which include external of permitting men to work therein.

19. 'I'he method of claim 17, in which the coolant is directly sprayed on the hot rolls openly y MICHAEL C. VINTI-IER. l 

